It is important to remember that a mysqlnd plugin is itself a PHP extension.
The following code shows the basic structure of the MINIT function that will be used in the typical mysqlnd plugin:
/* my_php_mysqlnd_plugin.c */ static PHP_MINIT_FUNCTION(mysqlnd_plugin) { /* globals, ini entries, resources, classes */ /* register mysqlnd plugin */ mysqlnd_plugin_id = mysqlnd_plugin_register(); conn_m = mysqlnd_get_conn_methods(); memcpy(org_conn_m, conn_m, sizeof(struct st_mysqlnd_conn_methods)); conn_m->query = MYSQLND_METHOD(mysqlnd_plugin_conn, query); conn_m->connect = MYSQLND_METHOD(mysqlnd_plugin_conn, connect); }
/* my_mysqlnd_plugin.c */ enum_func_status MYSQLND_METHOD(mysqlnd_plugin_conn, query)(/* ... */) { /* ... */ } enum_func_status MYSQLND_METHOD(mysqlnd_plugin_conn, connect)(/* ... */) { /* ... */ }
Task analysis: from C to userspace
class proxy extends mysqlnd_plugin_connection { public function connect($host, ...) { .. } } mysqlnd_plugin_set_conn_proxy(new proxy());
Process:
PHP: user registers plugin callback
PHP: user calls any PHP MySQL API to connect to MySQL
C: ext/*mysql* calls mysqlnd method
C: mysqlnd ends up in ext/mysqlnd_plugin
C: ext/mysqlnd_plugin
Calls userspace callback
Or orginal mysqlnd method, if userspace callback not set
You need to carry out the following:
Write a class "mysqlnd_plugin_connection" in C
Accept and register proxy object through "mysqlnd_plugin_set_conn_proxy()"
Call userspace proxy methods from C (optimization - zend_interfaces.h)
Userspace object methods can either be called using call_user_function() or you can operate at a level closer to the Zend Engine and use zend_call_method().
Optimization: calling methods from C using zend_call_method
The following code snippet shows the prototype for the zend_call_method function, taken from zend_interfaces.h.
ZEND_API zval* zend_call_method( zval **object_pp, zend_class_entry *obj_ce, zend_function **fn_proxy, char *function_name, int function_name_len, zval **retval_ptr_ptr, int param_count, zval* arg1, zval* arg2 TSRMLS_DC );
Zend API supports only two arguments. You may need more, for example:
enum_func_status (*func_mysqlnd_conn__connect)( MYSQLND *conn, const char *host, const char * user, const char * passwd, unsigned int passwd_len, const char * db, unsigned int db_len, unsigned int port, const char * socket, unsigned int mysql_flags TSRMLS_DC );
To get around this problem you will need to make a copy of zend_call_method() and add a facility for additional parameters. You can do this by creating a set of MY_ZEND_CALL_METHOD_WRAPPER macros.
Calling PHP userspace
This code snippet shows the optimized method for calling a userspace function from C:
/* my_mysqlnd_plugin.c */ MYSQLND_METHOD(my_conn_class,connect)( MYSQLND *conn, const char *host /* ... */ TSRMLS_DC) { enum_func_status ret = FAIL; zval * global_user_conn_proxy = fetch_userspace_proxy(); if (global_user_conn_proxy) { /* call userspace proxy */ ret = MY_ZEND_CALL_METHOD_WRAPPER(global_user_conn_proxy, host, /*...*/); } else { /* or original mysqlnd method = do nothing, be transparent */ ret = org_methods.connect(conn, host, user, passwd, passwd_len, db, db_len, port, socket, mysql_flags TSRMLS_CC); } return ret; }
Calling userspace: simple arguments
/* my_mysqlnd_plugin.c */ MYSQLND_METHOD(my_conn_class,connect)( /* ... */, const char *host, /* ...*/) { /* ... */ if (global_user_conn_proxy) { /* ... */ zval* zv_host; MAKE_STD_ZVAL(zv_host); ZVAL_STRING(zv_host, host, 1); MY_ZEND_CALL_METHOD_WRAPPER(global_user_conn_proxy, zv_retval, zv_host /*, ...*/); zval_ptr_dtor(&zv_host); /* ... */ } /* ... */ }
Calling userspace: structs as arguments
/* my_mysqlnd_plugin.c */ MYSQLND_METHOD(my_conn_class, connect)( MYSQLND *conn, /* ...*/) { /* ... */ if (global_user_conn_proxy) { /* ... */ zval* zv_conn; ZEND_REGISTER_RESOURCE(zv_conn, (void *)conn, le_mysqlnd_plugin_conn); MY_ZEND_CALL_METHOD_WRAPPER(global_user_conn_proxy, zv_retval, zv_conn, zv_host /*, ...*/); zval_ptr_dtor(&zv_conn); /* ... */ } /* ... */ }
The first argument of many mysqlnd methods is a C "object". For example, the first argument of the connect() method is a pointer to MYSQLND. The struct MYSQLND represents a mysqlnd connection object.
The mysqlnd connection object pointer can be compared to a standard I/O file handle. Like a standard I/O file handle a mysqlnd connection object shall be linked to the userspace using the PHP resource variable type.
From C to userspace and back
class proxy extends mysqlnd_plugin_connection { public function connect($conn, $host, ...) { /* "pre" hook */ printf("Connecting to host = '%s'\n", $host); debug_print_backtrace(); return parent::connect($conn); } public function query($conn, $query) { /* "post" hook */ $ret = parent::query($conn, $query); printf("Query = '%s'\n", $query); return $ret; } } mysqlnd_plugin_set_conn_proxy(new proxy());
PHP users must be able to call the parent implementation of an overwritten method.
As a result of subclassing it is possible to refine only selected methods and you can choose to have "pre" or "post" hooks.
Buildin class: mysqlnd_plugin_connection::connect()
/* my_mysqlnd_plugin_classes.c */ PHP_METHOD("mysqlnd_plugin_connection", connect) { /* ... simplified! ... */ zval* mysqlnd_rsrc; MYSQLND* conn; char* host; int host_len; if (zend_parse_parameters(ZEND_NUM_ARGS() TSRMLS_CC, "rs", &mysqlnd_rsrc, &host, &host_len) == FAILURE) { RETURN_NULL(); } ZEND_FETCH_RESOURCE(conn, MYSQLND* conn, &mysqlnd_rsrc, -1, "Mysqlnd Connection", le_mysqlnd_plugin_conn); if (PASS == org_methods.connect(conn, host, /* simplified! */ TSRMLS_CC)) RETVAL_TRUE; else RETVAL_FALSE; }